With conventional mechanical seals used in, for example, aircraft engine gearboxes, lubricating oil, which is a sealed fluid on an upstream side, penetrates between the sealing surfaces of a stationary side and a rotating side, forming an ultrathin film and lubricating the borders. When the upstream side is high in pressure, the lubricating oil between the sealing surface is pushed out to the downstream side by the pressure, causing leakage. When axial vibration is excessive, there is additional leakage in the axial direction in relation to the shaking of the rotating-side sealing surface, the space between the sealing surfaces widens, and the fluid leaks therein. To counter this, when an axial pressure force from a spring or the like is increased, the ultrathin oil film between the sealing surfaces becomes thinner and leakage is suppressed, but this approaches solid lubrication or direct contact; therefore, the amount of abrasion becomes excessive and the device becomes less durable. The sliding torque also becomes excessive, and the load on the device increases. Other problems also arise, such as the need to increase the rate of cooling flow.
To provide a function for controlling the thickness of the lubricating film covering, which is the sealed fluid, and also controlling the leakage amount of the sealed fluid, there is known in the art a sliding material in which a hard film covering is formed on the surface of an annular underlying metal material, and numerous dimples having a substantially consistent cross-sectional shape are formed over the entire sliding surface in a systematic alignment pattern; for example, substantially elliptical dimples 60 μm in width and 120 μm in length, whose major diameters are inclined 45° in relation to the sliding direction, are formed in the sliding surface at a surface area ratio of 8% relative to the surface area of the sliding surface, as shown in FIG. 20 (hereinbelow referred to as Prior Art 1, see Patent Document 1, for example).
According to Prior Art 1, the thickness of the lubricating film covering and the amount of sealed fluid leakage are controlled by the dimples formed in the sealing surface, and sliding characteristics similar to fine ceramics can be achieved, depending on the abrasion resistance of the sliding surfaces.
In another known sliding component (hereinbelow referred to as “Prior Art 2,” see Patent Document 2, for example), to reduce the coefficient of friction of the sliding surface and reduce leakage of the sealed fluid in the sliding surface, the sliding surface has a plurality of long, thin dimples which are separated by a border reference line and which have different inclined directions between those on the outer periphery side and those on the inner periphery side, as shown in FIG. 21, wherein the tips in the rotational direction of the outer periphery dimples are inclined toward the outer periphery while the tips in the rotational direction of the inner periphery dimples are inclined toward the inner periphery. The flat surface of each dimple is an elliptical or rectangular shape, for example, having a width of 50×10−6 m to 1000×10−6 m, a length of twice the width or more and ½ the width of the sliding surface or less, and a depth of 1×10−6 m to 25×10−6 m.
According to Prior Art 2, the expected effect is that a thick lubricating film covering of the sealed fluid will be maintained on the sliding surface between outer periphery dimples and inner periphery dimples, which would improve sealing performance.
In yet another known sliding component (hereinbelow referred to as “Prior Art 3,” see Patent Document 3, for example), to reduce the coefficient of friction of the sliding surface and reduce leakage of the sealed fluid in the sliding surface, the sliding surface has a first sliding surface on the side of the sealed fluid and a second sliding surface on the side opposite the sealed fluid, the first sliding surface has a plurality of at least one type of elliptical or rectangular dimples which are inclined relative to a direction tangential to the rotation of the circle, in the direction in which the longitudinal tips approach the peripheral surface on the side of the sealed fluid, as shown in FIG. 22. Each dimple is formed such that the longitudinal maximum width is 100×10−6 m or greater and 1000×10−6 m or less; the transverse length is 500×10−6 m or greater, greater than the width of the dimple, and less than the radial width of the first sliding surface; and the groove depth of each dimple is formed to be 1×10−6 m or greater, up to 25×10−6 m. The second sliding surface has a flat surface.
According to this Prior Art 3, the expected effects are that the coefficient of friction of the sliding surface will be reduced by the lubricating film covering maintained on the dimpled first sliding surface, the lubricating film covering present on the first sliding surface will be sealed by the second sliding surface, and the sealing performance of the sealed fluid will be improved by the second sliding surface while the lubricating effect is maintained by the lubricating film covering.